ISIS Militants Besiege Iraq's Largest Oil Refinery

BAGHDAD — Islamist militants laid siege to Iraq's largest oil refinery Wednesday, threatening a facility key to the country's domestic supplies as part of their ongoing lightning offensive, a top security official said.

The attack comes as militants have seized wide swaths of territory in Iraq — and as the specter of the sectarian warfare that nearly tore the country apart and the doubts that followed the 2003 U.S.-led invasion now haunt those trying decide how to respond.

The official said fighters of the al Qaeda-inspired Islamic State of Iraq and al-Sham (ISIS) began their attack on the Beiji refinery, some 155 miles north of Baghdad late Tuesday night. The attack continued into Wednesday morning, with fighters targeting it with mortar shells. A small fire started on the facility's periphery, he said.

The official spoke on condition of anonymity because he was not authorized to speak to journalists.

The Beiji refinery accounts for a little more than a quarter of the country's entire refining capacity — all of which goes toward domestic consumption for things like gasoline, cooking oil and fuel for power stations.

Any lengthy outage at Beiji risks long lines at the gas pump and electricity shortages, adding to the chaos already facing Iraq.

The Sunni militants of the Islamic State have vowed to march to Baghdad and the Shiite holy cities of Karbala and Najaf in the worst threat to Iraq's stability since U.S. troops left. The three cities are home to some of the most revered Shiite shrines. The Islamic State also has tried to capture Samarra north of Baghdad, home to another major Shiite shrine.

Some 275 armed American forces are being positioned in and around Iraq to help secure U.S. assets as President Barack Obama also considers an array of options for combating the Islamic militants, including airstrikes or a contingent of special forces.

The White House has continued to emphasize that any military engagement remains contingent on the government in Baghdad enacting political reforms and ending sectarian tensions, which had been on the rise even before the Islamic State's incursion last week, with thousands killed since late last year.